Adaptive control of mould compressibility

ABSTRACT

In a mold producing foundry machine generally according to the “Disamatic®”-principle a method of compensating for relatively slowly varying compaction properties of the mold particle material without compromising the geometrical requirements for repeatedly fixed placements of the pattern plates defining the mold chamber before the shot, comprises previous establishment of a beneficial set of starting parameters for shot and pressing of the mold to a fix terminating compaction force. The percentual volume reduction from the fixed starting volume to the terminating volume of the compacted mold—yielding the mold compressibility—is compared to the previously established beneficial reference value and the succeeding shots are adaptively controlled to compensate for the realised offset in compressibility by especially regulating the shot pressure, duration and fluidization parameters in a cyclic sequence securing steady reduction of the offset value to be within acceptable margins. The invention also comprises a related apparatus.

TECHNICAL FIELD

The present invention relates to a method for producing a series ofcasting moulds or flaskless substantially horisontally stack-able mouldparts, generally according to the commonly well known“Disamatic®”-principle, taking into account relatively slowly varyingcompaction properties of the particle material used.

The present invention also relates to an apparatus for carrying out themethod of the present invention.

BACKGROUND ART

The compaction properties is of importance in producing moulds of asuitable compactness. A loosely compacted (i.e. too low compactionratio) mould will easily be damaged during handling before casting orduring the casting operation itself. A low compacted mould might thusresult in defective castings or in leaks of molten metal damaging theequipment. On the other hand an excessively compacted (i.e. too highcompaction ratio) mould will have a low gas permeability consequentlyendangering entrapment of gases in the castings, thus creatingporosities or even hazardous mould blow-outs.

PRIOR ART

A method of the kind specified in the preamble is known from U.S. Pat.No. 5,332,025-A (Larsen). According to this method, compensation for thedrift in compaction properties of the particle material used consists inthe volume of the moulding chamber being measured/computed, before andafter the compacting step of the brought in particle material. Thevalues obtained are used to calculate a compaction ratio, which iscompared to a desired compaction ratio, yielding basis for makingadjustments of the production parameters (especially lengthsize of mouldchamber volume ready for filling and/or and compacting pressure) for thenext mould (part). In this manner it is possible to achieve a continuouscompensation for the drift in compacting properties.

Even though a reference compaction ratio value previously has beenestablished for a given set of pattern plates actually correspondinglylining respectively the two movable opposed walls in the generallybox-shaped mould chamber, and this reference value is used for the aboveparameter adjustments, the cited prior art method results in a majordrawback as the lengthwise “floating” character of the adjustable“before the shot” mould chamber volume is conflicting with requirementsfrom intricate pattern plates, especially with substantially overhangingpattern sections, which demand specific placement compared to theparticle material inlet to secure adequate material depositionespecially in the “shadowed” regions below overhangs during theintroduction of the particle material (i.e. “during the shot”).

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a method tocontrol production of moulds with adaptively optimized compressedparticle material pouring/degassing characteristics, taking into accountthe drift in compaction properties of the particle material used,without compromising the geometrical requirements dictated from theparticular set of pattern plates currently in use, namely geometricalrequirements both to initial size and placement relative to the particlematerial inlet of the closed not-yet-filled mould chamber volume, and tothe compressed volume of the resulted mould.

To this purpose the term “mould compressibility” is Introduced meaningthe reduction percentage from the first of the two just mentionedvolumes to the latter thereof (i.e. (volumes difference)/(initialvolume) %).

In other words the object of the method according to the presentinvention is to provide moulds with realized “mould compressibility”values corresponding to a previously established specific referencevalue, whereas the detected deviation value (i.e. “the offset”)adaptively is used as an input to control parameters to furtherreduce/keep at minimum the offset in the detected mould compressibilityvalue for moulds to be subsequently produced by controlling the step ofparticle material introduction into the mould chamber.

The present invention also relates to an apparatus for carrying out themethod of the present invention.

The advantages of the present invention consists in remedy of thementioned drawbacks by elimination to minimum of the variations incompacted mould quality resulting from the relatively slowly varyingcharacter of the properties of the particle material used, obeying atthe same time the geometrically related requirements dictated from theset of pattern plates actually in use, the present invention thusyielding more uniform quality of successive moulds, more uniform qualitycastings, and safer foundry operation.

An apparatus generally according to the “Disamatic®”-principle is fittedwith the pattern plates actually constituting a given set ofcorresponding pattern plates lining respectively the two movable opposedwalls in the generally box-shaped mould chamber in the apparatus.

According to the present invention:

1.a: The movable walls are, along their common axis of linear motion,placed at individually specific positions, relative to a particlematerial introduction (theoretical, reference) “point”, thus defining aspecific position for each of the pattern plates, such position beingreproducible and being previously established as being beneficial. Theplacements to this set of specific starting positions is performedbefore each new “shot” (introduction of particle material) into themould chamber, meaning the mould chamber has the same volume andposition relative to the material introduction “point” before eachsucceeding shot.

2.a: Particle material is introduced into the mould chamber defined asjust revealed, the amount of introduced material being controlled byespecially the duration of the shot and/or the driving gas pressure,these values initially being set according to beneficial referencevalues previously established as preferable starting values, thesevalues later being possibly adjusted according to a dominating adaptivecontrolling procedure.

3.a: Pressing of the Introduced particle material by relative approachof the movable walls according to known procedures, the pressing stepterminating at a specific pressing force/pressure, i.e. a fixed valuepreviously being established as beneficial.

4.a: Determination of the volume of the just pressed mould bydetermination of the distance between the movable walls aftertermination of the pressing step.

5.a: Dislocation of the just pressed mould for later pouring with moltenmaterial, according to known procedures, ending with the movable wallsagain defining the mould chamber according to above paragraph ref. 1.a.

5.b1: Calculating the resulted compressibility of the just pressed mouldand the compressibility offset relative to the previously establishedbeneficial reference value for the desired mould compressibility.

5.b2: According to an adaptive procedure determination of the possiblynecessary adjustment(s) of the parameter(s) for shot duration and/orshot driving gas pressure(s) to reduce to/keep within specified limitingvalues the compressibility offset expected for the next mould produced.

5.b3: Adjusting the apparatus according to the decisions in ref. 5.b2.

6.a: Repeating the steps from ref. 2.a, executing a next shot withpossibly adjusted parameters.

—.c: Terminating the loop between ref. 2.a and ref. 6.a at a suitableposition/point of time in the operation cyclus of the apparatus.

In the above paragraphs the numerical prefix is dominating the suite ofexecution of the operations mentioned; different letter suffixes to samenumber indicate individual “strings” of operations, that are executed“in parallel”, whereas a numerical suffix to a letter Indicate theplacement in the series covered by that letter suffixing a specificnumber.

Of course, necessary secondary operations are also required to carry outthe above method according to the present invention, e.g. storing ofvalues, introduction of offset/reference values specific to theapparatus and pattern plates used, measuring, calculating, usingconversion factors, algorithms and tables, decision and controllingactions (logical as physical), etc, besides the operation of theapparatus as such. These evident operations are known to the personsskilled in the art and will not be further discussed In the presentapplication.

Advantageous embodiments of the method and of the apparatus according tothe present invention are revealed in the appending claims and/or areexplained in the following detailed portion of the present specificationwith reference to the belonging drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The drawing accompanying this application consists of 3 figures,whereras:

FIG. 1 shows a diagrammatic flow-chart, illustrating the steps of themethod according to the present invention;

FIG. 2 shows, in vertical section, a schematic cut-out of an apparatusaccording to the present invention performing the method according tothe present invention, in the situation just before introduction ofparticle material, the opposed movable walls thus indirectly definingthe before-shot mould chamber volume, previously being established asbeing beneficial to the pattern plates used;

FIG. 3 shows, in vertical section, the cut-out apparatus of FIG. 2 atthe termination of the pressing step of the particle materialIntroduced, the opposed movable walls now indirectly defining the volumeof the compacted mould, used for calculating the resultedcompressibility of the mould, etc.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is related to a foundry machine functioning according tothe generally well known “Disamatic®”-principle; should the reader beunfamiliar with such apparatus and the functioning thereof, explanationcan be found in the above mentioned U.S. Pat. No. 5,332,025.

Hereinafter the reader is assumed being familiar with the overallprinciples and functioning related to the “Disamatic®”-tern; these willtherefore not be further discussed here.

In FIG. 1 the method according to the present invention is schematicallyshown as a flow-chart with the significant steps noted in respective“boxes”; the direction from top to bottom of the drawing plane of FIG. 1can qualitatively be taken as an axis of progressing time, thecorresponding minor steps within parallel series of steps being rankedvia the suffixed letters and digits as explained earlier.

The following description of the steps in FIG. 1 will be given withreference to the physical “world”, which via the schematic machine indifferent situations is illustrated in FIGS. 2 and 3, thus giving athorough understanding of the invention.

Re. FIG. 1 the action specified in the box representing the step a.1 ofthe method according to the present invention has resulted in, see FIG.2, placement of the first 2 and the second 3 movable walls of theapparatus 1 according to the “Disamatic®”-principle in respectivepositions at respective sides to the particle material inlet opening 11,thus by the space between the opposed surfaces of the pattern plates 9,10 defining a mould chamber 6, which of volume and position relative tothe inlet opening 11 has been found beneficial to this set of patternplates 9, 10 actually lining the movable walls 2, 3 respectively. Thebeneficial mould chamber size and position is mainly influenced by thegeometrical shapes of the opposed surfaces of the set of pattern platesactually used, as e.g. a pattern with a substantially protrudingoverhang, as seen on plate 9, results in difficulty in effectivelyfilling the bottom area below, that is “shadowed” from the inlet opening11 by the overhang, thus possibly requiring the mould chamber size andposition being optimized by moving the wall 2 with the adjacent patternplate 9 to a new resting position to the left in FIG. 2. Other importantparameters influencing the beneficial size and position are theproperties of the sand utilized and the pressures and their durations ofthe driving and fluidizing gas in the pressurizable material hopper 12during the introduction of particle material 7 from the hopper 12 intothe mould chamber 6. The goal is to achieve an adequate material fillingeverywhere of the beneficial volume yielding a high quality mould (partsblock) after pressing. Therefore the beneficial volume size and positionare correlated to optimum values of the pressure and time parameters ofthe “shot” for an actual profile of sand properties.

The set of beneficial/optimal values is often established duringlaboratory-type simulating tests remote from the actual pouring line.Preferably, the determination of the beneficial parameter set might bebettered, if the tests are carried out on a machine similar to themachine used for production, and most preferably such tests areperformed on the actual production machine supplied with sand ofproduction type and quality to give the most realistic determination ofthe set of beneficial setting-values.

The beneficial volume and position of the mould chamber 6 are indirectlyestablished by monitoring the absolute positions along their common axisof linear movement of the two movable walls 2, 3 by means of the twodetectors 13, 14 respectively. Thus the beneficial size and position ofthe mould chamber are established before each shot by controlling themovement of each movable wall 2, 3 to stop at the absolute position 4, 5respectively. Knowing the machine-size-defined fix height and fix width(perpendicular to the drawing plane of FIG. 2) of the mould chamber 6,the real size of the volume, e.g. expressed in the unit dm³, is easilycalculated from the absolute spacing in the length direction between thepositions 4 and 5 taking into account biasing by the fix length offsetsto the opposed surfaces of the movable walls 2, 3 and by the geometricalvolume of the pattern plates mounted adjacently.

Next the shot (FIG. 1, box 2.a) is performed, during which the particlematerial 7 in the hopper 12 by means of the driving gas and thefluidizing gas is forced from the hopper 12 through the inlet opening 11into the mould chamber 6 as illustrated with respective arrows in FIG.2. During the shot the pressures and durations of the driving andfluidizing gas are controlled according to a “receipt” and thebeneficial values earlier established.

Turning now to FIG. 1 box 3.a and FIG. 3, the brought in particlematerial in the mould chamber is compressed to a relatively solid block8 by relatively approaching the movable walls 2, 3. Such compressionterminating the pressing step, when the fix ending pressing force (thatcould be related to a pattern-plate-dependant fix hydraulic pressure ina cylinder exerting a force on a piston of fix geometry) no longer causerelative movement of the two movable walls 2, 3. The actual terminatingabsolute positions 16, 17 in the length direction of the movable walls2, 3 respectively are measured using the respective detectors 13, 14once more.

Known movements, etc. necessary to dislocate the mould 8 from themachine 1 and reposition the movable walls 2, 3 to once more define thebeneficial size and position of the mould chamber 6 (see FIG. 1 again)by being stopped at respective positions 4, 5 are now executed re. FIG.1 box 5.a. Before a next shot particle material is possibly also addedinto the hopper 12 through a top supply opening 18, which especiallyduring a shot can be closed and sealed by controlled use of known meansnot further discussed here. This step 5.a of the method according to thepresent invention is terminating by the machine 1 being physicallyprepared for a next shot into a mould chamber 6 of same beneficial sizeand position as the previous one.

During the execution of step 5.a a series of especially calculating,deciding and adjusting actions are performed at the control-system-levelof the machine 1. Whatever the kind of the control system (not furtherdetailed here), according to the invention at least the compressibilityof the just produced mould 8 is calculated by relating the actual set ofpressing-terminating readings 16, 17 from the detectors 13, 14 to thefix initial volume of the mould chamber 6, represented by the fixposition-values 4, 5 corrected from biasing fix length and fix volumecomponents. Thus the mould compressibility defined as (volumesdifference)/(initial volume) % of the just produced mould is calculatedand a value set representing the result is stored. In step/box 5.b1(FIG. 1) also the offset of the just calculated compressibility from abeneficial compressibility value, which also has been evaluated duringprevious (laboratory-like) tests, is calculated by the control systemand stored by some representative data set. Re. step/box 5.b2 next,resulting from some adaptively operating algorithm(s) working on therecently realized offset value(s) in relation to the set of establishedbeneficial relevant parameter values, later adaptations hereof caused bypreviously decided parameter adjustments according to the presentinvention, and an offset tolerance band, representing the desired mouldequality during the mould production run, is worked out a decisionwhether to adjust shot parameter(s) or not. After the calculations anddecisions in step 5.b2, the decided possible adjustments are executed instep 5.b3 of the method according to the invention. The generalprinciple for the adjustments prescribes:

-   a) realised compressibility value too high→more intense compaction    of particle material shot into the mould chamber required→augmented    driving pressure, change in fluidizing behavior and/or longer shot    duration required;-   b) realised compressibility value too low→less intense compaction of    particle material shot into the mould chamber required→reduced    driving pressure, change in fluidizing behavior and/or shorter shot    duration required; and-   c) realised compressibility OK→possible reduction of shot duration    by corresponding adjustment of fluidizing behavior and/or driving    pressure or other “local” optimization.

In FIG. 1 the step 6.a of the method according to the present inventionsecures, that the physical and the logical activities are syncronisedbefore the next shot is executed.

After this first cycles through the diagram in FIG. 1, the methodaccording the present invention prescribes successive cycles carried outuntil the cycling is interrupted by a system monitoring for “flags”signaling stop of performing the method. Such flags might representsecurity warnings or emergency stop signals. Also shift in compositionof poured metal and/or properties of supplied particle material mightrequire intermediate stop of performance of the method to give in a newbeneficial value for intended compressibility and/or mould chambersize/position.

As the duration of the shot normally is a dominating component directlyaffecting the overall cycle time of the machine 1 and as the ever-wantedoptimization of the production normally is demanding minimization ofcycle time, the above adaptive algorithms preferable might be organizedin a hierarchy to first consume the possible reserve of “pressure”and/or “fluidizing” adjustments, before precious extra time for the shotduration is “consumed”. If the drift of the properties of the sanddelivered to the hopper 12 is of a relatively permanent character, theadaptive algorithms might need to shift between different parameters tofirst be “used up” by the successive adjustments intermediating thesuccessive shots.

The exemplary embodiment shown in the figures are, of course, onlyintended to illustrate the principles of the present Invention withoutdelimiting the scope thereof. Thus the method according to the presentinvention might be carried out in many different embodiments of anapparatus according to the present invention, such embodiment alsocomprising retrofitment to a machine, not hitherto being able to performthe method of the invention, of neccessary extra means allowing forrealising the method according to the present invention, the scope ofwhich is defined by the appending claims.

REFERENCE NUMBERS

-   1 apparatus, according to Disamatic®-principle-   2 first movable wall-   3 second movable wall-   4 specific (start) position,(2)-   5 specific (start) position,(3)-   6 mould chamber-   7 particle material (in hopper)-   8 pressed mould-   9 pattern plate, lining first wall-   10 pattern plate, lining second wall-   11 particle material inlet opening to mould chamber-   12 pressurizable material hopper-   13 detector, absolute linear position-   14 detector, absolute linear position-   15 pressing piston extension-   16 measured position, pressing ended-   17 measured position, pressing ended-   18 top supply opening, hopper

1. A method of producing a series of casting moulds or flasklesssubstantially horizontally stack-able mould parts in a series of cyclesof operations of an apparatus fitted with a given set of correspondingpattern plates lining respectively two movable opposed walls in thegenerally box-shaped mould chamber in the apparatus, said method takinginto account relatively slowly varying compaction properties of aparticle material used over the series of cycles and securing a desiredmould compressibility of the moulds or mould parts produced each cycle,said method comprising the following steps during each cycle ofoperation:
 1. placing the opposed movable walls along a common axis oflinear motion at individually specific wall starting positions relativeto a particle material introduction reference point, the placing stepthus defining an individually specific pattern starting position foreach of the pattern plates which individual pattern starting positionhas been previously established as being beneficial and thus determiningthe wall starting positions; the placing step of the movable walls tothe individually specific wall starting positions being performed eachcycle and before a shot of particle material is introduced into themould chamber, such that the mould chamber has a same volume andposition relative to the material introduction point before eachsucceeding shot of each cycle;
 2. introducing of a shot of particlematerial into the mould chamber located at the individually specificwall starting positions, the introducing step controlling the amount ofthe shot of the particle material by controlling a parameter selectedfrom one of a duration of the shot or a driving gas pressure profile ofthe shot, the introducing step initially controlling the parameteraccording to a beneficial reference starting parameter previouslyestablished as preferable, the parameter in succeeding cycles beingadjusted as set forth hereafter;
 3. pressing of the introduced shot ofthe particle material to form a mould by relative approach of themovable walls toward each other, the pressing step terminating at aspecific pressing force/pressure, which is a fixed value previouslybeing established as beneficial;
 4. determining of a volume of the justpressed mould by determining of a distance between the movable wallsafter termination of the pressing step,
 5. dislocating of the justpressed mould for later pouring with molten material, the dislocatingstep ending with the movable walls again defining the mould chamber inaccordance with step 1.; 5.b1 calculating a resulted compressibility ofthe just pressed mould and a compressibility offset relative to thedesired mould compressibility; 5.b2 adjusting, in response to thecalculated resulted compressibility, the parameter as necessary in orderto cause the compressibility offset expected for a next mould producedto be within specified limiting values; 5.b3 adjusting the apparatusaccording to any necessary adjustments determined in step 5.b2; and 6.repeating the steps starting at step
 1. 2. The method according to claim1, wherein the adaptive procedure used during step 5.b2 results in anynecessary adjustment being made to the driving gas pressure profile,with the shot duration being kept unaltered.
 3. The method according toclaim 2, wherein the adaptive procedure used during step 5.b2 results inany necessary adjustment for one driving gas pressure of the driving gaspressure profile, the shot duration and possibly other driving gaspressures being kept unaltered.
 4. The method according to claim 1,wherein the driving gas pressure profile is time-dependant.